Hi Guys. I am using Dir-842 and received UNIFI 500Mbps Turbo Upgrade.

I can get roughly 450~470Mbps on LAN. However, when I use my smartphone (a Redmi 5 Plus) on the 5Ghz connection, I could only get about 90~100Mbps when sitting right next to the router. Is this speed considered normal? I thought this is an AC1200 Router?

My DIR-842's WiFi is very unstable. The phone keeps losing connection and gets reconnected every time. I wonder any other users facing the same problem?

But that's a router I just bought last month. I just want to know is this phenomenon normal?

Nope. I goes with default setting when I setup my router. Will try and see whether this works.